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| Term | Description |
|---|---|
| Thermal conductance (C) | The time rate of steady-state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces. In English (inch•pound) units of measurement, the number of British thermal units (Btu) that pass through a specified thickness of a 1-square-foot sample of material in one hour with a temperature difference between the two surfaces of 1 degree Fahrenheit. In English (inch•pound) units, it is expressed as Btu/h•ft2•F.
Note 2: It is mathematically incorrect to multiply or divide the thermal conductance (C) value for a specific thickness of a material to determine the thermal conductance value of a different thickness of the same material. Note 3: It is mathematically incorrect to add thermal conductance (C) values to determine overall thermal performance. If it is necessary to determine the overall thermal performance of a construction, it is appropriate to convert the individual thermal conductance (C) values to thermal resistance (R) values (i.e., R = 1/C) and then add the thermal resistance values (i.e., Rt = R1 + R2 + ...). |